The invention relates to brake mechanisms for electric motors and the like.
The invention arose during continuing development efforts relating to motor brakes such as shown in U.S. Pat. Nos. 4,798,269, 4,181,201, 4,042,077, 3,878,922, 3,556,266, 3,525,424 and 3,500,971, and as shown in "Stearns Spring-Set Disc Brakes", Catalog No. 200 68910M, Stearns Division, Rexnord Corporation, 1989, and "Stearns Spring-Set Disc Brakes Installation and Service Instructions for Series 48,000", Sheet 300.10A, effective Mar. 21, 1989, page S-700-1, P/N8-078-924-05, Stearns Division, Rexnord Corporation.
The brake mechanism selectively stops or permits rotation of a shaft journaled in the motor frame. One or more friction discs secured to the shaft rotate therewith about the axis of the shaft. An end plate is secured to the motor frame, and has one or more non-rotatable pressure plates mounted thereto for axial movement toward and away from the friction discs. A lever is mounted to the end plate for pivotal movement about bearing surfaces toward and away from the pressure plates. Compression springs bias the lever against the pressure plates such that the pressure plates engage the friction discs and prevent rotation of the motor shaft. A solenoid is secured to the end plate and has a reciprocally movable plunger connected to the lever and movable to a first position moving the lever in one axial direction away from the pressure plates against the bias of the compression springs to release the friction discs and permit rotation of the shaft. The plunger is movable to a second position permitting the lever to move under the bias of the compression springs in the opposite axial direction toward and engaging the pressure plates such that the pressure plates engage the friction discs and prevent rotation of the shaft. This basic structure is common in the industry.
The present invention provides improvements in simplification, cost reduction, ease of maintenance, and enhanced performance and life.
In one aspect of the invention, retention structure is provided permitting quick and easy removal and replacement of the friction discs. Rather than disassembling the entire brake mechanism or substantial portions thereof, only a single bolt need be removed in order to remove and replace the friction discs. This substantially reduces maintenance and service time.
In another aspect of the invention, simplified structure is provided for accepting low force compression springs biasing the pressure plates away from the friction discs in the released condition of the brake to minimize brake drag otherwise caused by contact of the pressure plates and friction discs during rotation of the motor shaft. In vertically mounted orientations of the motor brake, the gravitational weight of the pressure plates themselves may cause brake drag against the friction discs during rotation of the motor shaft. It is known in the prior art to secure leaf springs to the end plate to minimize brake drag. It is also known in the prior art to provide low force compression springs around pins secured to the end plate for performing such function, as shown in "Stearns Spring-Set Disc Brakes Parts List for 55,000 Series", PTC Sheet 309, Oct. 31, 1985, page S-607-1, FlGS. H, I, J, K, and L. In the latter embodiment, the brake must be specially modified by drilling holes in the end plate and in outer tabs of the pressure plates, and inserting pins into such holes, which pins receive the low force compression springs. The present invention accepts low force compression springs without modification of the brake mechanism.
In another aspect of the invention, resilient shock absorbers are provided on studs mounting the solenoid to the end plate. The shock absorbers perform two functions. Firstly, the shock absorbers absorb mechanical shock from the plunger at the end of its travel stroke as it seats against the solenoid abutment surface. Inclusion of the shock absorbers has been found to reduce breakage of parts, which is believed otherwise due to the forceful snap of the plunger. Secondly, the shock absorbers allow simple positioning of the solenoid to minimize solenoid buzz. The solenoid is subject to buzz if the plunger does not seat flushly against the solenoid abutment surface due to the connection of the plunger to the lever. In the prior art, a lock nut on a stud adjusts the position of the solenoid bracket, and another nut on the opposite side of the bracket is tightened to hold the solenoid in place. During adjustment, two wrenches are typically used, one to loosen the nut below the bracket, and the other to tighten the nut above the bracket, or vise versa. In the present invention, the noted second function of the shock absorbers eliminates the two nut and wrench adjustment sequence, and instead only requires a single wrench and nut tightening adjustment.
In another aspect of the invention, part content is reduced by eliminating separate studs otherwise required for mounting the brake mechanism cover. Instead, the studs mounting the high force compression springs are also used to mount the brake mechanism cover.
In another aspect of the invention, improved bearing action and reduced bearing cost is provided. Hardened drive pins with rounded heads are secured to the end plate and provide substantially point contact and smooth pivotal bearing movement of the lever.
In another aspect of the invention, a simplified manual brake release is provided which accommodates one or two friction disc brakes and maintains the desirable function of automatically resetting upon energization of the solenoid, such that when the solenoid is deenergized the brake is effective to stop rotation of the motor shaft.